In the past, when a piezoelectric element such as a piezoelectric actuator has been manufactured, a mother piezoelectric substrate has been prepared so as to increase productivity. This mother piezoelectric substrate has been divided, and separated into individual fractional piezoelectric elements. Incidentally, when a piezoelectric element has been manufactured, a poling treatment has been performed in the stage of a mother piezoelectric substrate. Accordingly, when, on a substrate or the like, a piezoelectric element has been mounted that has been obtained by dividing and separating the mother piezoelectric substrate into individual fractions, it has been necessary to confirm the polarization direction of the piezoelectric element and mount the piezoelectric element so that the polarization direction has become a correct polarization direction.
So as to confirm the polarization direction of such a piezoelectric element as described above, a structure illustrated in FIG. 9 has been used in Patent Document 1 described below. FIG. 9 is a perspective view illustrating a piezoelectric element 1001 of the related art.
In the piezoelectric element 1001 illustrated in FIG. 9, a first electrode 1003 is formed on the top surface of the piezoelectric substrate 1002. In the center of the first electrode 1003, a through hole 1004 is formed. On the other hand, in the entire bottom surface of the piezoelectric substrate 1002, a second electrode 1005 is formed so as to face the first electrode 1003. In the second electrode 1005, no through hole is provided. In addition, the piezoelectric substrate 1002 has been subjected to a poling treatment in a thickness direction as indicated by an arrow illustrated in the drawing.
In the piezoelectric element 1001, since the above-mentioned through hole 1004 is provided in the first electrode 1003, it is possible to identify a polarization direction. In other words, when the mass-produced piezoelectric element 1001 is observed from the outside, it is possible to identify the polarization direction on the basis of the presence or absence of the through hole 1004.
In addition, in Patent Document 2, a manufacturing method described below has been disclosed. First, electrodes are formed on the entire surfaces of both main surfaces of a mother piezoelectric substrate. Next, the mother piezoelectric substrate is subjected to a poling treatment. After doing that, a groove is formed in one of the electrodes of the both main surfaces of the mother piezoelectric substrate. Next, the mother piezoelectric substrate is divided, and a large number of piezoelectric elements are obtained that have been separated into fractions.    Patent Document 1: Japanese Unexamined Utility Model Registration Application Publication No. 61-75631    Patent Document 2: Japanese Unexamined Patent Application Publication No. 11-94555